The history of metal (and non-metal) surface mass finishing is based on various modes regarding the method through which the mass constituted by the media and the pieces is moved.
The first known mode in modern times (after the second world war) is that of the rotary tumbler, a cylindrical vat subjected to a rotary movement, within which the moving mass rolls, developing a typical “wave” movement on whose descending ramp there develops an interesting slide of the pieces, with extremely valid finishing levels, revealing the drawback of not being very fast.
This method is common up to date, for example, in some processes such as optical glasses finishing process.
In the 60's Dr. Manfred Dreher, from Pforzheim, Germany, started off with the first solution of the satellite tumbler though he abandoned the vertical solution after various experiments. The Dreher satellite tumblers, obtained using horizontal barrels, allow optimal finishing levels as well as very low process times.
This solution then spread all over the world and, currently, it represents one of the most common techniques in Asian countries. The movement within barrels is partly similar to that of the tumbler, but accelerated within the times and in the centrifuge forces developed therein. Furthermore, right from the 60s, the first series of uses with pieces mounted (thus fixed) on a framework is associated to this type of “mass finishing” technique, while a finishing “media” incoherent mass finishing rotates therearound.
From this primordial concept there are obtained perfect pieces, without dents (like it may occur should one leave them in a free mass) and having smooth and shiny surfaces.
Even today many finishings obtained using satellite tumblers cannot be equalled, in the quality/cost ratio of the finishing process, with other known systems.
However a first drawback of this technique lies in the capacity of the machines, which can have extremely large dimensions.
A second drawback lies in the difficulty of loading and unloading, barrel by barrel.
A third considerable drawback lies in the difficulty of forming multi-step cycles, for example with intermediate rinsing operations, given that each would require a manual intervention opening the barrels one by one, and so on and so forth, this being another reason why they are more common in Asia, for example, than in Europe.
The late sixties and the early seventies marked the introduction of the first machines constituted by vibrant vats both of the toroid or circular type and of the linear or rectangular type. This system replaces the rotary tumbler in many applications, due to the considerable flexibility of use, the greater automation, the lower water demand with respect to a tumbler in the wet type of process, the ideal operating mode for the wet and dry processing (extremely common processes), as well as for drying using plant grains.
The seventies and eighties marked the introduction of the first spindle finishing machines constituted by a rotary vat containing the finishing media and the pieces supported by rotary spindles fixed to robust inclinable mechanical arms for the loading and unloading operations. These techniques initially became extremely common in the United States of America and they still are up to date, with machines increasingly quicker, sophisticated and protected in terms of safety.
A drawback regarding the use of this type of technique regards the poor productivity; regardless of the speed and efficiency of the processes actually there can be loaded two pieces per cycle, by hand.
Around the early eighties there were introduced the first Japanese, American and European machines of the rotary disc centrifuge type (disc finishing). They offer advantages analogous to the vibration finishing solution but with quicker times as long as the processed pieces are not very large. The use limit thereof is the cost of the spare discs, which are extremely high in some cases.
Various applications arise, also in this solution, by holding the pieces fixed to some devices (for example a rotary shaft), exposing it to the flow of the media in quick rotation. The companies that applied this technique mainly included Polish and Italian companies that generally operate in the jewellery industry.
Probably still in the eighties the German constructor Walther Trowal introduced drag finishing machines, mostly used without vibrating, with very large vats and rotary heads with large rotary spindles where the pieces to be subjected to finishing are submerged.
Large distribution in the nautical industry (propellers for marine engines), in the medical industry, in the aerospace industry, boost this technology. Shortly later some constructors exploited the very same finishing principle providing machines with static vat. Each of these machines represent the state of the art and the frequency of application based on vibrating vats is very limited, if not entirely unused.
Early in 2011 the German company Otec Präzisionsfinish GmbH proposed a machine very similar, if not identical in the mode of the finishing media mass, arranged in a rotary vat, to that of the aforementioned spindle finishing. The machine is slightly different from the modern spindle finish (for example Almco Finishing and Cleaning Systems—USA) due to the criterion of positioning the spindles, which allows loading and unloading the pieces even while the machine is operating.
This system—also referred to as stream finishing—is quite complex from a mechanical point of view and it is based on an indexed head which supports rotary spindles. The head may perform a vertical excursion for prospecting the pieces supported by the rotary spindles to the finishing media mass rotating in the vat.
The rotary vat adopted in the known techniques, such as for example the spindle finishing, allows entry to one or more spindles in a mass constituted by the finishing media.
In the example in which an article should be subjected to two or more finishing media such as, for example a roughing media, a smoothening media and a polishing media, the machines operating according to the prior art, would require translating the spindle from one vat to the other or, alternatively, having only one machine with only one vat, replacing the roughing media with the smoothing ones, and subsequently, the smoothing one with the polishing ones.